Magnetic recording medium, manufacturing method thereof, and magnetic recording/reproducing apparatus

ABSTRACT

A magnetic recording medium has a RAM region and a ROM region. The RAM region includes a plurality of first tracks each having a first magnetic portion. The first magnetic portions in adjacent tracks are separated from each other. The ROM region includes a plurality of second tracks each having a second magnetic portion. A width of the second magnetic portions in a direction perpendicular to a track direction of the first tracks is larger than that of the first magnetic portions in the perpendicular direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic recording medium, amanufacturing method thereof, and a magnetic recording/reproducingapparatus, and more particularly, to a magnetic recording medium havinga rewritable RAM (Random Access Memory) region and an unrewritable ROM(Read Only Memory) region, a manufacturing method of the magneticrecording medium, and a magnetic recording/reproducing apparatusincluding the magnetic recording medium.

2. Description of the Related Art

In response to demand for an increase in storage capacity, a recentmagnetic recording device, a magnetic disk drive, and a hard disk drivemust increase recording density of a magnetic recording medium. However,in association with an increase in recording density, there is arising aproblem that magnetic information recorded by a read/write head, whichmoves over the medium relatively, affects recording of an adjacenttrack. There has been proposed a countermeasure for avoiding such aproblem by physically separating magnetic substances in adjacent tracks(see, e.g., JP-A-Sho. 62-256225).

Magnetic substances on a magnetic recording medium are patterned torecord t servo information and ROM information according to presence orabsence of the magnetic substances (see, e.g., JP-A-Hei. 10-255407).

The method for patterning a magnetic substance on a magnetic recordingmedium includes, for example, a nanoimprint method. This method firstdraws and develops a desired pattern of magnetic substances as anirregularity pattern on a master disk by using a rotary disk writingsystem. Next, this method forms an imprint stamper onto which theirregularity pattern on the surface of the master disk are transferred,from the master disk. Then, the method presses the imprint stamperagainst a resist film applied over the recording medium, therebytransferring the irregularities on the surface of the stamper to theresist film. Finally, the method transfers the irregularities on thesurface of the resist film to a lower recording layer by means of atechnique, such as etching, to thus pattern the magnetic substances.

BRIEF SUMMARY OF THE INVENTION

However, results of inventors' study show that when an attempt is madeto implement a magnetic recording medium having a RAM region and a ROMregion by using the thus-patterned magnetic substances, signals obtainedfrom the respective regions are different from each other in terms ofsignal intensity, thereby rendering reading operation difficult.

The invention has been made in view of this problem and provides amagnetic recording medium having a ROM region and a RAM region fromwhich data can be read with superior signal intensity, as well asproviding a method for manufacturing the magnetic recording medium and amagnetic recording/reproducing apparatus.

In order to solve the problem, according to one embodiment of theinvention, a magnetic recording medium has a RAM region and a ROMregion. The RAM region includes a plurality of first track search havinga first magnetic portion. The first magnetic portions in adjacent tracksare separated from each other. The ROM region includes a plurality ofsecond tracks each having a second magnetic portion. A width of thesecond magnetic portions in a direction perpendicular to a trackdirection of the first tracks is larger than that of the first magneticportions in the perpendicular direction.

According to one embodiment of the invention, a magnetic recordingapparatus has the magnetic recording medium as set forth above and aread/write head. The read/write head moves relatively to the magneticrecording medium, records information into the magnetic recordingmedium, and reproduces the information recorded in the magneticrecording medium.

According to one embodiment of the invention, in the magnetic recordingapparatus, the read/write head writes a magnetization pattern into thesecond magnetic portions of the ROM region of the magnetic recordingmedium.

According to one embodiment of the invention, a method for manufacturinga stamper for a magnetic recording medium, includes applying a resistfilm onto a substrate having a RAM region and a ROM region; drawing witha plurality of exposure beam lines on the resist film applied onto thesubstrate, x lines of the exposure beam lines corresponding to groovesof the stamper in the RAM region to form each of first tracks of the RAMregion, y lines of the exposure beam lines corresponding to grooves ofthe stamper in the ROM region to form each of second tracks of the ROMregion, wherein the exposure beam lines extend in a track direction andx<y; transferring an exposed pattern onto the substrate; andtransferring a transferred pattern of the substrate to the stamper.

Also, according to one embodiment of the invention, a method formanufacturing a master disk for a magnetic recording medium, includesapplying a resist film onto the master disk having a ROM region and aRAM region; drawing with a plurality of exposure beam lines on theresist film applied onto the master disk, x lines of the exposure beamlines corresponding to ridges of the master disk in the RAM region toform each of first tracks of the RAM region, y lines of the exposurebeam lines corresponding to ridges of the master disk in the ROM regionto form each of second tracks of the ROM region, wherein the exposurebeam lines extend in a track direction and x<y; and transferring anexposed pattern onto the master disk.

According to the embodiment of the invention, in the magnetic recordingmedium having the ROM region and the RAM region, a good balance can beachieved between a signal reproduced from the ROM region and a signalreproduced from the RAM region. Moreover, it is possible to provide anauthentication region. Further, it is also possible to nullify andinitialize the ROM region.

Consequently, there can be provided a magnetic recording medium havinghigh recording density and capable of storing various types ofauthentication data and reliably reproducing the data, thereby offeringa large industrial merit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram exemplifying a part of the planarstructure of a magnetic recording medium according to an embodiment ofthe invention.

FIG. 2 is a schematic diagram exemplifying, as a comparative example ofthe invention, a part of the planar structure of a magnetic recordingmedium reviewed during the course of the inventors having come toconceive the invention.

FIGS. 3A and 3B are schematic diagrams for describing signal intensityobtained from a RAM region of the magnetic recording medium according tothe embodiment of the invention.

FIGS. 4A and 4B are schematic views for describing signal intensityobtained from a ROM region 100 of the magnetic recording mediumaccording to the comparative example;

FIGS. 5A and 5B are schematic diagrams for describing signal intensityobtained from a ROM region of the magnetic recording medium according tothe embodiment of the invention.

FIG. 6 is a schematic diagram illustrating a part of the planarstructure of a magnetic recording medium of a patterned medium accordingto an embodiment of the invention.

FIG. 7 is a schematic diagram illustrating a part of the planarstructure of a magnetic recording medium according to another embodimentof the invention.

FIG. 8 is a schematic diagram illustrating a part of the planarstructure of a magnetic recording medium according to an embodiment ofthe invention.

FIG. 9 is a schematic diagram illustrating a part of the planarstructure of a magnetic recording medium according to the embodiments ofthe invention.

FIG. 10 is a schematic diagram for describing a method for initializingthe ROM region 11 of the magnetic recording medium according to theembodiments of the invention.

FIG. 11 is a schematic diagram for explaining nullification of the ROMregion 11 of the magnetic recording medium according to the embodimentsof the invention.

FIG. 12 is a schematic view for describing a method for writing datainto the magnetic recording medium according to the embodiments of theinvention.

FIG. 13 is a schematic diagram illustrating a method for manufacturing amagnetic recording medium according to the embodiments of the invention.

FIGS. 14A to 14D are schematic diagrams illustrating processes formanufacturing a magnetic recording medium according to the embodimentsof the invention.

FIGS. 15A to 15C are schematic diagrams illustrating processes formanufacturing a magnetic recording medium according to the embodimentsof the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will be described hereinbelow withreference to the drawings.

FIG. 1 is a schematic diagram exemplifying a part of a plane structureof a magnetic recording medium according to an embodiment of theinvention. This magnetic recording medium has a RAM region 10 and a ROMregion 11.

In the RAM region 10, a plurality of magnetic portions 13 arecontinuously arranged to extend in a longitudinal direction of tracks.In the RAM region 10, the magnetic portions 13 in adjacent tracks arephysically separated from each other. Specifically, a width L2 of themagnetic portion 13 when viewed in a direction perpendicular to thelongitudinal direction of the tracks is smaller than a track width T2.Area other than the magnetic portions 13 is formed from a nonmagneticportion 14. Specifically, strips of the magnetic portions 13 and stripsof the nonmagnetic portions 14 are alternately arranged in the RAMregion 10.

On the other hand, in the ROM region 11, a plurality of magneticportions 15 are intermittently arranged in the longitudinal direction ofthe tracks. Intervals between the magnetic portions 15 within a singletrack are not uniform, and the magnetic portions 15 are arrangedintermittently. In the case of a specific example shown in FIG. 1, themagnetic portions 15 in adjacent tracks remain in physical contact witheach other. Namely, a width L1 of the magnetic portion 15 when viewed inthe direction perpendicular to the longitudinal direction of the tracksis equal to a track width T1. In the ROM region 11, areas other than themagnetic portions 15 are formed of the nonmagnetic portions 14.

In this embodiment, the track width T1 in the ROM region 11 and thetrack width T2 in the RAM region 10 are equal to each other. The widthL1 of the magnetic portions 15 in the ROM region 11 is broader than thewidth L2 of the magnetic portions 13 in the RAM region 10.

FIG. 2 is a schematic diagram exemplifying, as a comparative example,apart of the planar structure of a magnetic recording medium studiedduring the course of the present inventor having come to conceive theembodiment of the invention. Specifically, in this magnetic recordingmedium, magnetic portions in all the regions are equal in width to eachother. This magnetic recording medium has the RAM region 10 and a ROMregion 100.

In the RAM region 10, the plurality of magnetic portions 13 arecontinuously arranged to extend in the track direction. In the RAMregion 10, magnetic portions 101 in adjacent tracks are physicallyseparated from each other. In short, the width L2 of the magneticportion 13 when viewed in the direction perpendicular to thelongitudinal direction of the tracks is smaller than the track width T2.Since areas other than the magnetic portions 13 are the nonmagneticportions 14, strips of the magnetic portions 13 and strips of thenonmagnetic portions 14 are alternately arranged in the RAM region 10.

When data are recorded in the RAM region 10, a write head (not shown)moves over the magnetic portion 13 in parallel to the longitudinaldirection of the tracks and sequentially changes the magnetizationdirections of the magnetic portions 13, to thus perform recordingoperation. At the time of reproducing operation, a read head (not shown)moves over the magnetic portions 13 in parallel to the longitudinaldirection of the tracks and sequentially reads magnetic fieldscorresponding to the magnetization directions of the magnetic portions13, to thus perform reproducing operation. Specifically, the directionsof magnetization of the magnetic portions 13 in the RAM region 10 areclassified into a first direction and a second direction, which is areversal thereof.

A plurality of magnetic portions 101 are intermittently arranged in theROM region 100 in the longitudinal direction of the tracks. Intervalsbetween the magnetic portions 101 in a single track are not uniform, andthe magnetic portions 101 are arranged intermittently. The magneticportions 101 in adjacent tracks are physically separated from each otherin the ROM region 100, as well. Namely, a width L10 of the magneticportions 101 when viewed in the direction perpendicular to thelongitudinal direction of the tracks is smaller than a track width T10.In the ROM region 100, areas other than the magnetic portions 101 areformed of the nonmagnetic portions 14.

When the data of the ROM region 100 are reproduced, the read head (notshown) moves over the magnetic portions 101 and sequentially readsmagnetic fields from the intermittently-provided magnetic portions 101,to thus perform reproducing operation. Magnetization of all the magneticportions 101 in the ROM region 100 is usually aligned in a singledirection. Hence, data are often recorded by means of physicalarrangement of the magnetic portions 101.

In the magnetic recording medium shown in FIG. 2, the width L10 of themagnetic portions 101 in the ROM region 100 is equal to the width L2 ofthe magnetic portions 13 in the RAM region 10. The track width T10 inthe ROM region 100 is also equal to the track width T2 in the RAM region10.

As mentioned above, when data are reproduced from the magnetic recordingmedium in which the RAM region 10 and the ROM region 100 having the samewidth of the magnetic portions are mixedly present, by means of a singleread/write head, there arises a problem that signals derived from therespective regions are different in intensity from each other. Morespecifically, magnetic portions having two types of reversedmagnetization directions exist in the RAM region 10. Hence, when anattempt is made to read data from the RAM region 10 by using an MR(Magnetoresistance Effect) or a GMR (Giant Magnetoresistance Effect)head, the thus-read signal is converted into an electric current flowingthrough the element. The intensity of the thus-obtained signal fallsbetween +1 and −1. In contrast, the magnetization direction of themagnetic portions 101 in the ROM region 100 is constant. Further, thewidth L10 of the magnetic portions 101 in the ROM region 100 is equal tothe width L2 of the magnetic portions 13 in the RAM region 10. Hence,the intensity of the obtained signal falls within a range between +1 and0.

Specifically, the signal read by the read head assumes +1 and −1 in theRAM region 10 in which the magnetic portions 13 have two types ofreversed magnetization directions. Therefore, signal amplitudes having adifference of 2 (two) are obtained. In contrast, in the ROM region 100in which the magnetic portions 101 have a constant magnetizationdirection, there are produced a signal +1 and a signal 0. Namely, thesignal amplitudes assume 1 (one). Accordingly, a signal obtained fromthe ROM region 11 in which provided are the magnetic portions 101 havingthe same width as that of the magnetic portions 13 in the RAM region 10has a smaller signal amplitude required for identification in comparisonwith the RAM region 10. Hence, there arises a problem that it isdifficult to read the signals obtained from the ROM region 100.

In the meantime, as shown in FIG. 1, in this embodiment, the width L1 ofthe magnetic portion 15 in the ROM region 11 is made larger than thewidth L12 of the magnetic portion 13 in the ROM region 10. Therefore, itis possible to facilitate reading signals from the ROM 11.

FIGS. 3 to 5 are schematic diagrams for describing signal intensityobtained from the magnetic recording medium according to the embodimentof the invention and that obtained from the magnetic recording medium ofthe comparative example.

FIGS. 3A and 3B is schematic diagrams for describing signal intensityobtained from the RAM region 10 of the magnetic recording mediumaccording to the embodiment of the invention. FIG. 3A shows the planarstructure of the RAM region 10 of the magnetic write head according tothe embodiment of the invention. In the RAM region 10 shown in FIG. 3A,magnetic portions 13 a having a magnetization direction for imparting asignal +1 to a read head 18 and magnetic portions 13 b having amagnetization direction for imparting a signal −1 to the read head 18are arranged to extend in the longitudinal direction of the track.Intervals between the magnetic portions 13 a in a single track are notnecessarily uniform, and the magnetic portions 13 b are arrangedintermittently. Specifically, the width L2 of the magnetic portions 13when viewed in the direction perpendicular to the longitudinal directionof the track is smaller than the track width T2. Areas other than themagnetic portions 13 a, 13 b are formed of the nonmagnetic portions 14.

As shown in FIG. 3B, signals are sequentially output in the RAM region10 in accordance with movement of the read head 18, whereby a signal,which oscillates between signal intensity +1 and signal intensity −1, isobtained. An obtained amplitude is 2.

FIGS. 4A and 4B are schematic views for describing signal intensity ofthe ROM region 100 of the magnetic recording medium of the comparativeexample. In short, FIG. 4A shows a planar structure of the ROM region100 of the comparative example shown in FIG. 2. As shown in FIG. 4A, themagnetic portions 101 having a magnetization direction for imparting asignal +1 to the read head 18 are intermittently arranged in thelongitudinal direction of the track. Intervals between the magneticsubstances 100 in a single track are not uniform, and the magneticportions 101 are arranged intermittently. In the ROM region 100, themagnetic portions 101 in adjacent tracks are physically separated fromeach other. That is, the width L10 of the magnetic portion 101 whenviewed in the direction perpendicular to the longitudinal direction ofthe track is smaller than the track width T10. Areas of the ROM region100 other than the magnetic portions 101 are formed of the nonmagneticportions 14. The width L10 of the magnetic portions 101 in the ROMregion 100 is equal to the width L2 of the magnetic portion 13 in theRAM region 10. The track width T10 of the ROM region 100 is also equalto the track width T2 of the RAM region 10.

As shown in FIG. 4B, in the ROM region 100 in which the magneticportions 101 are equal in width to the magnetic portions 13 in the RAMregion 10, signals are sequentially output in accordance with movementof the read head 18, whereby signals, which oscillate at a signalintensity between +1 and 0, are obtained. That is, the amplitude of theobtained signal is as small as 1 (one).

FIGS. 5A and 5B are schematic diagrams for describing signal intensityin the ROM region 11 of the magnetic recording medium according to theembodiment of the invention. FIG. 5A shows a planar structure of the ROMregion 11 in which the magnetic portions 15 are greater in width thanthe magnetic portions 13 in the RAM region 10. As shown in FIG. 5A, themagnetic portions 15 having such a magnetization direction as to imparta signal of positive sign to the read head 18 are fully arranged in thewidth direction of the track. That is, the magnetic portions 15 inadjacent tracks remain in physical contact with each other in the ROMregion 11. The width L1 of the magnetic portions 15 in the directionperpendicular to the tracks is equal to the track width T1. The areasother than the magnetic portions 15 are formed of the nonmagneticportions 14. At this time, the width L1 of the magnetic portions 15 inthe ROM region 11 is greater than the width L2 of the magnetic portions13 in the RAM region 10. The track width T1 is equal to the track widthT2.

As shown in FIG. 5B, signals are sequentially output in accordance withmovement of the read head 18 in the ROM region 11 in which the magneticportions 15 are greater in width than the magnetic portions 13 in theRAM region 10. At this time, the width L1 of the magnetic portions 15 isgreater than the width L2 of the magnetic portions 13 (FIG. 1). Hence, asignal having an intensity greater than +1 is obtained. Namely, signalsobtained from the ROM region 11 in which the width L1 of the magneticportions 13 is greater than that L2 of the magnetic portions 13 in theRAM region 10 oscillate between a signal intensity 0 corresponding tonon-magnetic portions 14 and signal intensity +1 obtained from themagnetic portions 15. The amplitude of the resultantly obtained signalbecomes greater than 1.

When the signal intensity obtained from the RAM region 10 shown in FIG.3 is compared with that obtained from the ROM region 100 of thecomparative example shown in FIG. 4, the signal intensity obtained fromthe ROM region 100 of the comparative example has come to substantiallyone-half that obtained from the RAM region 10. Therefore, it isdifficult to distinguish the signal intensity obtained from the ROMregion 100 of the comparative example. In contrast, as exemplified inFIG. 5, since the width of the magnetic portions 15 in the ROM region 11is broadened, the intensity of the signal that the read head 18 receivesfrom the magnetic portions 15 can be made greater. In this case, on theassumption that the signal intensity obtained from the RAM region 10 istaken as “+1,” the signal intensity obtained from the ROM region 11 inwhich the magnetic portions 15 are wider in width than those 13 of theRAM region 10 becomes greater than “+1”.

In the magnetic recording medium according to the embodiment of theinvention, by broadening the width of the magnetic portions in the ROMregion, a difference in signal intensity (signal amplitude)substantially equal to that achieved in the RAM region is obtained.Since sufficiently-high signal intensities are obtained from both of theRAM region and the ROM region, it is possible to record/reproduce datainto/from the RAM region and to reproduce data from the ROM region.

When the recording/reproduction apparatus is used, all of the magneticportions 15 in the ROM region 11 are magnetized in a given directionwith respect to the direction of the track. The read/write head 18 doesnot perform recording of data into the ROM region 11. Accordingly, thedata recorded in adjacent tracks are not adversely affected from eachother during recording operation. Therefore, in order to achieve highrecording density, the magnetic portions 13 in the RAM region 10 must beseparated from each other by reducing the width L2 of the magneticportions 13 in adjacent tracks. In contrast, since the write head 18does not need to perform writing operation into the ROM region 11 duringthe course of usage of the recording/reproduction apparatus, the widthL1 of the magnetic portions 15 can be broadened up to the track widthT1.

As mentioned above, according to the magnetic recording medium of theembodiment of the invention, data can be reproduced from the ROM region11 and the RAM region 10 with a sufficient signal intensity ratio byincreasing the width L1 of the magnetic portions 15 in the ROM region 11to be broader than the width L2 of the magnetic portions 13 in the RAMregion 10.

The magnetic recording medium according to the embodiment of theinvention has a feature that all the regions have the same track width.

On condition that all of the regions have the same track width,prediction and control are easy to carry out when the read/write head ismoved to an arbitrary track. In the magnetic recording medium accordingto the embodiment of the invention, the width of the magnetic portionschanges from one region to another region. If the width of the track ischanged in accordance with the width of the magnetic portions, it isdifficult to position the head to the tracks during therecording/reproducing operation. Therefore, the magnetic recordingmedium according to the embodiment of the invention has a feature thatan interval between adjacent tracks; i.e., the track width of therespective regions, is uniform. Namely, in the medium according to theembodiment of the invention, the track intervals are constant and onlythe widths of the magnetic portions are different in each region.

FIG. 6 is a schematic diagram illustrating a part of the planarstructure of a magnetic recording medium of a patterned medium accordingto an embodiment of the invention. This magnetic recording medium hasthe RAM region 10 and the ROM region 11. Specifically, magnetic portionsof the magnetic recording medium are so-called “patterned mediums”, andadjacent magnetic portions are not in contact with each other. The“patterned mediums” used herein refer to magnetic portions not onlyphysically separated from each other if they are in adjacent tracks, butalso separated from each other in the longitudinal direction of thetracks.

In the RAM region 10, a plurality of magnetic portions 19 areintermittently arranged at given intervals in the longitudinal directionof the tracks. In the RAM region 10, magnetic portions in adjacenttracks are physically separated from each other. Specifically, the widthL2 of the magnetic portions 19 is smaller than the track width T2 whenviewed in the direction perpendicular to the longitudinal direction ofthe track. Areas other than the magnetic portions 19 are formed of thenonmagnetic portions 14.

On the other hand, in the ROM region 11, a plurality of magneticportions 20 are intermittently arranged at irregular cycles in thelongitudinal direction of the tracks. Specifically, the magneticportions 20 in the same track are not uniform and are arrangedintermittently. Even in the ROM region 11 of the specific example,magnetic portions in adjacent tracks remain in physical contact witheach other as described in connection with FIG. 1. Specifically, thewidth L1 of the magnetic portions 20 when viewed in the directionperpendicular to the longitudinal direction of the tracks is equal tothe track width T1. Areas other than the magnetic portions 20 in the ROMregion are formed of the nonmagnetic portions 14.

In this magnetic recording medium, the width L1 of the magnetic portions20 in the ROM region 11 is greater than the width L2 of the magneticportions 19 in the RAM region 10. The track width T1 in the ROM region11 is equal to the track width T2 in the RAM region 10.

As mentioned above, in the embodiment of the invention, the magneticportions may be patterned mediums. Data can be reproduced in both theROM region 11 and the RAM region 10 at a sufficient signal intensityratio so long as the width L1 of the magnetic portions 20 in the ROMregion 11 is greater than the width L2 of the magnetic portions 19 inthe RAM region 10.

FIG. 7 is a schematic diagram showing a part of the planar structure ofa magnetic recording medium according to another embodiment of theinvention. FIG. 7 shows the planar structure of the RAM region 10 andthat of the ROM region 11 in the magnetic recording medium.

In the RAM region 10, a plurality of magnetic portions 13 arecontinuously arranged to extent in the direction of the tracks. In theRAM region 10, the magnetic portions 13 in adjacent tracks arephysically separated from each other. Specifically, the width L2 of themagnetic portions 13 when viewed in the direction perpendicular to thelongitudinal direction of the tracks is smaller than the track width T2.Areas other than the magnetic portions 13 are formed of the nonmagneticportions 14. Hence, in the RAM region 10, strips of the magneticportions 13 and strips of the nonmagnetic portions 14 are arrangedalternately.

On the other hand, in the ROM region 11, a plurality of magneticportions 24 are intermittently arranged in the longitudinal direction ofthe tracks. Intervals between the magnetic portions 24 in a single trackare not constant, and the magnetic portions 24 are arrangedintermittently. In the ROM region 11, the magnetic portions in adjacenttracks are physically separated from each other. Specifically, a widthL3 of the magnetic portions 24 in the direction perpendicular to thetrack direction is smaller than the track width T1. In the ROM region11, areas other than the magnetic portions 24 are formed of thenonmagnetic portions 14.

In this magnetic recording medium, the width L3 of the magnetic portions24 in the ROM region 11 is greater than the width L2 of the magneticportions 13 in the RAM region 10. The track width T1 in the ROM region11 is equal to the track width T2 in the RAM region 10.

As mentioned above, even if the width L3 of the magnetic portions 24 inthe ROM region 11 is smaller than the track width T1 in the ROM region11, data can be reproduced with a sufficient signal intensity ratio inboth the RAM region 10 and the ROM region 11 so long as the width L3 ofthe magnetic portions 24 in the ROM region 11 is greater than the widthL2 of the magnetic portions 13 in the RAM region 10.

FIG. 8 is a schematic diagram showing a part of the planar structure ofa magnetic recording medium according to an embodiment of the invention.FIG. 8 shows the planar structure of the RAM region 10, that of the ROMregion 11 in the magnetic recording medium, that of a servo region 12,and that of an authentication region 17.

In the RAM region 10 in which data are recorded by magnetizationdirections of magnetic portions, the magnetic portions 13 arecontinuously arranged in parallel to the longitudinal direction of thetracks. In the ROM region 11 in which data are recorded byabsence/presence of magnetic portions, the magnetic portions 15 areintermittently arranged in parallel to the longitudinal direction of thetracks. The width L1 of the magnetic portions 15 in the ROM region 11 isgreater than the width L2 of the magnetic portions 13 in the RAM region10. Areas other than the magnetic portions are formed of the nonmagneticportions 14.

Positional data are recorded in a servo region 12 by presence/absence ofa magnetic portion 22. The magnetization directions of the magneticportions 22 are aligned in a given direction with respect to thedirection of the track. When a read head passes over the servo region 12in the approximate track direction, the positional information can beacquired. At least a preamble signal, an address signal, and apositioning burst signal are present in the servo region 12. The widthL4 of the magnetic portions 22 in the servo region 12 is greater thanthe width L2 of the magnetic portions 13.

In an authentication region 17, magnetic portions 21 are intermittentlyarranged in the longitudinal direction of the track, and data arewritten by means of both presence/absence of the magnetic portions 21and magnetization directions of the magnetic portions 21. In theauthentication region 17, the magnetic portions 21 are intermittentlyarranged in the direction of the track. On the basis of certain data,magnetization of the magnetic portions 21 can be changed. Specifically,at the time of authentication, the read head 18 moves over thearrangement of the magnetic portions 21, and the read head 18sequentially reads magnetic fields corresponding to presence/absence ofthe magnetic portion 21 and the magnetization direction of the magneticportions 21. The thus-read data are stored as “key data A”.

Subsequently, the write head 18 writes magnetization into the magneticportions 21 in accordance with a given rule.

Further, the read head 18 moves over the arrangement of magneticportions 21, and the read head 18 sequentially reads presence/absence ofthe magnetic portions 21 and the magnetic field from the magnetizationdirection of the magnetic portions 21. The thus-read data are stored as“key data B”. Authentication is performed through use of thethus-obtained “key data A” and “key data B”. In this specific example,the track width T1 of the ROM region 11, the track width T2 of the RAMregion 10, the track width T4 of the servo region 12, and the trackwidth T5 of the authentication region 17 may be made equal to eachother.

As mentioned above, in the authentication region 17, the magneticportions 21 are intermittently arranged in the longitudinal direction ofthe track as in the case of the ROM region 11. The write head recordsand writes data onto the magnetic portions during the authenticationoperation, whereupon recording is performed by means of themagnetization direction. Accordingly, in order to read data formed bypresence/absence of the magnetic portions, a larger width L5 of themagnetic substances is preferable, as in the case of the ROM region 11.However, in order to record the magnetization direction of the magneticportions, physical separation of adjacent strips of magnetic portions 21is preferred as in the case of the RAM region 10. Consequently, thewidth L5 of the magnetic portions 21 in the authentication region 17 ismade smaller than the width L1 of the magnetic portions 15 in the ROMregion 11. It is preferable that the width L5 of the magnetic portions21 in the authentication region 17 is smaller than the width L1 of themagnetic portions 15 in the ROM region 11 and that the width L5 of themagnetic portions 21 in the authentication region 17 is equal to orgreater than the width L2 of the magnetic portions 13 in the RAM region10.

It is noted that U.S. patent application Ser. No. 10/606,788 (publishedas US2004/0107355 A1) discloses a method for performing authenticationabout a magnetic recording medium in detail, entire contents of whichare incorporated herein by reference.

FIG. 9 is a schematic diagram showing a part of the planer structure ofa magnetic recording medium according to the embodiments of theinvention. As shown in FIG. 9, the toroidal RAM region 10 exists in theouter periphery of the disk, and the toroidal ROM region 11 exists inthe inner periphery of the disk. A plurality of sector-shaped servoregions 12 are radially present. The respective servo regions 12 arewritten radially with respect to the disk of the magnetic recordingmedium. In association with rotation of the disk, the read/write head 18on the track passes the servo region 12 at every given time intervals.

The RAM region 10 and the ROM region 11 are not mixedly present. Thatis, when concentrically viewed from above, the toroidal RAM region 10 ispresent at in outer periphery and the toroidal ROM region 11 is providedin the inner periphery. When the ROM region 11 of the magnetic recordingmedium according to the embodiments is initialized, an area to which anexternal magnetic field 32 is applied falls inside a specific circle.Hence, it is preferable that the ROM region 11 is disposed in the innerperiphery of the disk.

FIG. 10 is a schematic diagram for describing a method for initializingthe ROM region 11 of the magnetic recording medium according to theembodiments of the invention. As shown in FIG. 10, when the ROM region11 of the magnetic recording medium is initialized, the read/write head18 is retracted to the outside of the medium disk so that it isprevented that an external magnetic field destroys the read/write head18. A magnetic field 32 higher than the coercivity of the magneticportions is applied to the ROM region 11 of the disk, thereby aligningthe magnetization directions of the magnetic portiosn in the ROM region11.

When the ROM region is initialized by the external magnetic field, it ispreferable that a medium is of vertical recording type and that themagnetic field is applied in a direction perpendicular to the surface ofthe medium.

According to this initialization method, the servo regions 12 are alsoexposed to the external magnetic field 32. However, the magnetizationdirection of the magnetic portions in the servo regions 12 must bealigned. Hence no problem arises if the magnetization direction is thesame as that of the external magnetic field 32.

Specifically, it is preferable that the ROM region 11 of the magneticrecording medium according to the embodiments of the invention ismagnetized in a given direction with respect to the direction of thetrack. In the magnetic recording medium of the embodiments, the magneticfield 32 higher the coersivity of the magnetic portions is appliedexternally to the particular ROM region 11 of the recording medium toalign the magnetizations of the magnetic portions 15 in the ROM region11 at a time. Therefore, in comparison with a method for aligningmagnetizations by using a write head, this method can performinitialization faster. With regard to a range of magnetization, only theROM region may be initialized by applying a magnetic field solely to theROM region in the inner periphery of the medium, or the overall mediummay be initialized in one operation by applying a magnetic field to theentire medium.

FIG. 11 is a schematic diagram for explaining nullification of the ROMregion 11 of the magnetic recording medium according to the embodimentsof the invention. FIG. 11 shows magnetic portions in two adjacent trackswithin the ROM region 11. In the ROM region 11, the nonmagnetic portions14, magnetic portions 15 a having such a magnetization direction toimpart a signal +1 to the read head 18, and magnetic portions 15 bhaving such a magnetization direction to impart a signal −1 to the readhead 18 are intermittently arranged in the direction of the tracks.

Before nullification, the magnetization directions of the magneticportions 15 are aligned to +1 by means of the previously-describedinitializing method. In this state, the write head 18 moves over the ROMregion 11 while writing a certain signal pattern. If the position of thehead 18 is shifted slightly toward a track 2 so that data aremagnetically recorded on the magnetic portions in an area larger thanthe locus of the head, data having a magnetization direction of −1 arewritten into the magnetic portions 15 in the track 2 as shown in FIG.11.

Even when the read head 18 attempts to reproduce data from the track 1or track 2 after this operation, the data which the read head 18 hasattempted to read; that is, magnetization of the track 1 in direction −1and magnetization of the track 2 in direction +1, are not reproduced. Inthis case, data reproduced from a reproduction signal are unpredictable.Moreover, it is difficult to obtain data of the ROM region 11 at a timeof the initialization from the data of the reproduction signal. In thisstate, the ROM region 11 of the magnetic recording medium according tothe embodiments of the invention cannot be used for reading data of theROM region 11. In other words, the ROM region 11 is nullified.

As in the case of the RAM region 10, the write head 18 usually does notrecord or write data into the ROM region 11 of the magnetic recordingmedium according to the embodiments of the invention. Hence, the widthL1 of the magnetic portions 15 in the ROM region 10 may be made greaterthan the width L2 of the magnetic portions 13 in the RAM region 10.Therefore, when the write head 18 writes data into the ROM region 11,because the positional shift of the write head 18 and size of therecorded magnetization are large, magnetizations of the magneticportions 15 in adjacent tracks are affected. Therefore, even when theread head 18 reads signals from the ROM region 11 after the recordingand writing operations, there is little chance that data recorded by thewrite head 18 can be reproduced in their original forms.

As mentioned above, in the ROM region 11 of the magnetic recordingmedium according to the embodiments of the invention, the ROM region 11can be nullified by writing given data with the write head 18. As aresult, access to, e.g., the ROM region 11, can be prohibited at anarbitrary timing during use of the recording medium.

Even after having been nullified, the ROM region 11 can be used again,by means of employing the previously-described ROM region initializationmethod.

FIG. 12 is a schematic view for describing a method for writing datainto the magnetic recording medium according to the embodiments of theinvention. FIG. 12 shows a part of the planar structure of the RAMregion 10, the ROM region 11, the servo region 12, and theauthentication region 17 of the magnetic recording medium according tothe embodiments of the invention. As in the case of the magneticrecording medium shown in FIG. 8, in the magnetic recording medium shownin FIG. 12, the width L1 of the magnetic portions 15 in the ROM region11 and the width L4 of the magnetic portions 22 in the servo region 12are greater than the width L2 of the magnetic portions 13 in the RAMregion 10 and the width L5 of the magnetic portions 21 in theauthentication region 17, respectively.

As indicated drawing lines in FIG. 12, one track is written by fourdrawing lines arranged at uniform intervals. Of these drawing lines, thewidth of magnetic portions can be changed depending on number of thedrawing lines used for writing a magnetic substance pattern. Forinstance, in FIG. 12, the RAM region 10 is written by two drawing lines;the ROM region 11 is written by four drawing lines; and theauthentication region 17 is written by two drawing lines. Consequently,a structure having magnetic portions can be prepared in which widths ofthe magnetic portions in the RAM region and the authentication regionare about half of the track width, and widths of the magnetic portionsin the ROM region are substantially equal to the entire track width.

As mentioned above, under the method for drawing the magnetic recordingmedium according to the embodiments of the invention, the width of themagnetic portion can be changed by the manner of selecting the number ofdrawing lines used for drawing a master disk.

FIG. 13 is a schematic diagram showing a method for manufacturing amagnetic recording medium according to the embodiments of the invention.After a resist film has been applied onto a glass disk 25 having adiameter of 8 inches and a thickness of 5 mm by means of the spincoating method, the disk 25 is exposed to electrons 24 while beingrotated. At this time, a spot of the electrons 24 has a width of 50 nm.The master glass disk 25 is exposed to an electron beam while a positionto be exposed to the electron beam is shifted by 50 nm in the radialdirection of the master disk 25 every rotation of the master glass disk25. A track pitch is set to 200 nm, and one track is written by fourdrawing lines.

The drawn region is a range defined by an inner radius of 12 mm to 30mm, and 120 servo regions are provided over the entire perimeter of thedisk. The authentication region is a range defined by a radius of 12 mmto 13 mm. The ROM region is a range defined by a radius of 13 mm to 15mm. The RAM region is a range from 15 mm to 30 mm.

In the authentication region 17 and the RAM region 10, drawn are twocenter lines of the four drawing lines in the track. In the ROM region,all of the four drawing lines in the track are drawn. Data required toinstall an OS are written into the ROM region 11 while being encrypted.Data based on random numbers are written into the authentication region17.

Next, processes for manufacturing the magnetic recording mediumaccording to the embodiments of the invention will be described asanother embodiment of the invention.

FIGS. 14 and 15 are schematic diagrams showing processes formanufacturing the magnetic recording medium according to the embodimentsof the invention.

As shown in FIG. 14A, a resist film 26 for electron drawing is appliedover the glass master disk 25 to have a thickness of 100 nm by means ofthe spin coating method.

As shown in FIG. 14B, a pattern is drawn on the resist film 26 by meansof the electron beam 24. The electron beam is radiated onto positions ofthe recording medium, which would finally be nonmagnetic portions. Theglass master disk 25 is processed by a developing solution, whereby anirregular pattern is formed in the surface of the resist film 26 on theglass master disk 25. The positions exposed to the electron beam 24become a recessed pattern.

Subsequently, as shown in FIG. 14C, the glass master disk 25 is etchedin CF₄, thereby transferring the irregular pattern of the resist film 26to the glass master disk 25. Thus, a master disk 27 for producing animprint stamper is obtained. At this time, the irregular pattern formedin the surface of the master disk 27 has about 100 nanometers in depth.

Finally, as shown in FIG. 14D, the surface of the master disk 27 issubjected to nickel electroforming, to thus obtain an imprint stamper28. The depth of irregularities of the imprint stamper 28 is about 50nanometers.

As shown in FIG. 15A, a soft magnetic layer having a ruthenium alloy isformed on the toroidal glass disk 25, which has a radius of 65 mm and abore having an inner radius of 20 mm. A magnetic film 29 of verticalrecording type having a recording layer made of a cobalt alloy is formedon a surface of the soft magnetic layer by means of the sputteringmethod. A novolak-type resist 30 is applied to have a thickness of 70 nmby means of the spin coating method.

As shown in FIG. 15B, the imprint stamper 28 is pressed against theglass disk 25 for one minute at a pressure of 500 atm. Theirregularities in the surface of the imprint stamper 28 are transferredonto the resist film 30 on the surface of the glass disk 25.

As shown in FIG. 15C, the irregular pattern has been transferred on thesurface of the resist 30 such that an area from which magnetic portionsare to be finally removed has a depth of 50 nm.

The surface of this glass disk 25 is subjected to argon ion milling,thereby etching the resist film 30 and the magnetic film 29. Themagnetic film 29 is also removed from an area of the surface of theresist film 30 having a recessed structure, by means of milling. Inareas of the surface of the resist film 30 where no recess is formed,the resist film 30 is etched by milling, but etching fails to reach themagnetic film 29, whereby the magnetic portions are left.

The thus-obtained glass disk is subjected to oxygen ashing, therebyremoving the remaining resist 30. As a result, a pattern formed of themagnetic portions is obtained. A protective film is formed on thesurface of the glass disk by means of the carbon sputtering, to thusform a magnetic recording medium.

An example usage of the thus-obtained magnetic recording mediumaccording to the embodiments of the invention will now be described.

As mentioned previously in connection with FIG. 10, the magnetic field32 of 3000 Oe (oersted) is applied to the ROM region 11 of the magneticrecording medium, thereby initializing the ROM region 11. Further,random numbers differing from those recorded previously are written intothe authentication region 17 by means of an authentication regioninitializing device, thereby rendering the magnetic recording mediumusable.

The thus-initialized magnetic recording medium can be used in variousapplications.

For instance, this magnetic recording medium can be used as a diskinstalled with the OS (Operating System) of a computer. Specifically,the magnetic recording medium is built in the magnetic recordingapparatus. When the magnetic recording apparatus is built into acomputer, the read head 18 reads the authentication regions 17, to thusacquire the “key data A.” The write head 18 subsequently writes the datain the authentication region 17. Then, the read head 18 reads data fromthe same authentication region 17, thereby acquiring the “key data B.” A“cipher key K” is obtained from the “key data A” and the “key data B.”The encrypted OS install data written in the ROM region 11 are decryptedby the thus-obtained “cipher keyK.” The OS is installed in the RAMregion 10 of the recording medium such that the computer is activatedthrough use of the magnetic recording apparatus.

The width L1 of the magnetic substances in the ROM region 11 is greaterthan the width L2 of the magnetic substances in the RAM region 10, andhence a sufficient signal intensity ratio is ensured between the ROMregion 11 and the RAM region 10, whereby reproduction is performedwithout any problems.

After completion of installation of the OS, the write head 18 writes inthe ROM region 11 data consisting of an alternating sequence of, e.g.,10101010. Consequently, an overlap exists between adjacent tracks,thereby nullifying the ROM region 11. As a result, the recorded datacannot be reproduced in their original form. Subsequently, even when therecording apparatus is removed and the OS is installed through use ofanother personal computer, the data in the ROM region 11 cannot be read,thereby limiting the number of times the OS can be installed. In short,fraudulent copying of the OS can be prevented.

This advantage can also be applied to a system for renting a magneticrecording medium on which music or a video is recorded.

Specifically, a service dealer collects the magnetic recording apparatuswhose ROM region 11 is nullified, and the thus-collected magneticrecording apparatus is set on the apparatus for initializing the ROMregion 11. In the apparatus for initializing the ROM region 11, theread/write head 18 recedes to the outside of the disk, and the magneticfield 32 of 5000 Oe is applied to a circular range up to a radius regionof 15 mm of the recording medium, thereby aligning the magnetizationdirection on the medium. Moreover, the service dealer again writes thecipher data A in the authentication region 17 on the basis of the datapertaining to the authentication region 17 held by the service dealer.As a result, the ROM region 11 of the recording medium is initialized,whereby the ROM region 11 again becomes usable.

Thus far, the embodiments of the invention have been described withreference to the specific examples. However, the invention is notlimited to the specific examples. For instance, with regard to aspecific material forming the magnetic recording medium and filmthickness, geometry, and dimensions thereof, all materials, filmthickness, geometries, and dimensions-which enable practice of theinvention and yielding of the same advantage so long as one skilled inthe art makes appropriate selection-fall within the scope of theinvention.

In other respects, all magnetic recording mediums—which one skilled inthe art can achieve by appropriate design change on the basis of themagnetic recording medium described as the embodiments of theinvention—fall within the scope of the invention.

1. A magnetic recording medium comprising: a RAM region including aplurality of first tracks each having a first magnetic portion, thefirst magnetic portions in adjacent tracks being separated from eachother; and a ROM region including a plurality of second tracks eachhaving a second magnetic portion, a width of the second magneticportions in a direction perpendicular to a track direction of the firsttracks being larger than that of the first magnetic portions in theperpendicular direction.
 2. The magnetic recording medium according toclaim 1, wherein the first magnetic portions of the RAM region extendcontinuously in the track direction.
 3. The magnetic recording mediumaccording to claim 1, wherein the first magnetic portions of the RAMregion are arranged intermittently in the track direction.
 4. Themagnetic recording medium according to claim 1, a width of the firsttracks in the perpendicular direction is equal to that of the secondtracks in the perpendicular direction.
 5. The magnetic recording mediumaccording to claim 1, further comprising: an authentication regionincluding a third track having a third magnetic portion, a width of thethird magnetic portion in the perpendicular direction being smaller thanthat of the second magnetic portions of the ROM region in theperpendicular direction.
 6. The magnetic recording medium according toclaim 5, a width of the first tracks of the RAM region in theperpendicular direction, that of the second tracks of the ROM region inthe perpendicular direction, and that of the third track of theauthentication region are equal to each other.
 7. The magnetic recordingmedium according to claim 1, wherein the width of the second magneticportions of the ROM region in the perpendicular direction is equal tothat of the second tracks of the ROM region in the perpendiculardirection.
 8. The magnetic recording medium according to claim 1,wherein the width of the second magnetic portions of the ROM region inthe perpendicular direction is smaller than that of the second tracks ofthe ROM region in the perpendicular direction.
 9. A magnetic recordingapparatus comprising: a magnetic recording medium that comprises: a RAMregion including a plurality of first tracks each having a firstmagnetic portion, the first magnetic portions in adjacent tracks beingseparated from each other; and a ROM region including a plurality ofsecond tracks each having a second magnetic portion, a width of thesecond magnetic portions in a direction perpendicular to a trackdirection of the first tracks being larger than that of the firstmagnetic portions in the perpendicular direction; and a read/write headthat moves relatively to the magnetic recording medium, recordsinformation into the magnetic recording medium, and reproduces theinformation recorded in the magnetic recording medium.
 10. The magneticrecording medium according to claim 9, wherein the read/write headwrites a magnetization pattern into the second magnetic portions of theROM region of the magnetic recording medium.
 11. A method forinitializing at least a part of a magnetic recording medium, the methodcomprising: providing the magnetic recording medium that comprises: aRAM region including a plurality of first tracks each having a firstmagnetic portion, the first magnetic portions in adjacent tracks beingseparated from each other; and a ROM region including a plurality ofsecond tracks each having a second magnetic portion, a width of thesecond magnetic portions in a direction perpendicular to a trackdirection of the first tracks being larger than that of the firstmagnetic portions in the perpendicular direction; and applying magneticfield to the second magnetic portions of the ROM region, the magneticfield being larger than coercitivity of the second magnetic portions.12. A method for manufacturing a stamper for a magnetic recordingmedium, the method comprising: applying a resist film onto a substratehaving a RAM region and a ROM region; drawing with a plurality ofexposure beam lines on the resist film applied onto the substrate, xlines of the exposure beam lines corresponding to grooves of the stamperin the RAM region to form each of first tracks of the RAM region, ylines of the exposure beam lines corresponding to grooves of the stamperin the ROM region to form each of second tracks of the ROM region,wherein the exposure beam lines extend in a track direction and x<y;transferring an exposed pattern onto the substrate; and transferring atransferred pattern of the substrate to the stamper.
 13. A method formanufacturing a master disk for a magnetic recording medium, the methodcomprising: applying a resist film onto the master disk having a ROMregion and a RAM region; drawing with a plurality of exposure beam lineson the resist film applied onto the master disk, x lines of the exposurebeam lines corresponding to ridges of the master disk in the RAM regionto form each of first tracks of the RAM region, y lines of the exposurebeam lines corresponding to ridges of the master disk in the ROM regionto form each of second tracks of the ROM region, wherein the exposurebeam lines extend in a track direction and x<y; and transferring anexposed pattern onto the master disk.